The Celestial Spirit King who rules all of the spirit world and enforces the rules among all the spirits. He is the most powerful of all the spirits although it is unknown if he gives out his key to humans or even if he has one.

Aquarius states that he can only be summoned once by any Celestial Wizard who can do a three simultaneous zodiac key summoning. The other condition for summoning him is "Summoning with a Price." For the grave price of destroying Aquarius' key, Lucy summons the Celestial Spirit King. In doing so, Lucy is unable to see Aquarius ever again.